The present invention relates to an inflatable seat belt apparatus, more particularly to an inflatable seat belt, wherein a webbing of a seat belt apparatus to restrain an occupant has an inflatable portion formed in an envelope shape which is usually maintained in a band shape and is inflated, in an accident, in a predetermined shape with gas spouted from a gas generating means.
Presently, a seat belt apparatus is necessary for a vehicle or the like as an apparatus for securing an occupant's body, which restrains the occupant from sudden movement by a deceleration and an impact in a crash.
Such a seat belt apparatus comprises a webbing as a woven belt made of a fabric which has approximately a 50 mm width and is formed according to Japanese Industrial Standard, to have a retractor (hereinafter referred to ELR: Emergency Locking Retractor), a buckle, a tongue, an anchor and so on.
The ELR winds the webbing by a winding force of a spring and locks the webbing from withdrawing only at a crash so as to restrain the occupant. The buckle is mounted on a suitable position near a floor so that the webbing fits the occupant's body well.
Conventionally, the seat belt apparatus locks the webbing from withdrawing by the function of ELR at a crash to restrain the occupant from a forward movement.
For improvement in the efficiency of restraining the occupant, each of U.S. Pat. Nos. 3,841,645, 3,865,398, and 3,866,940 discloses a seat belt apparatus in which the webbing has a portion formed in an envelope shape and is folded like bellows. The portion is provided with a weak adhesive so as to usually maintain in a band shape, or the folded portion is held in the band shape by fastening means such as a fastener, so that in a crash, the portion formed in the envelope shape is inflated and deployed by a spouted gas from a gas generator connected to the webbing.
According to the seat belt apparatus having the inflatable portion formed in an envelope shape (hereinafter, it is called as "an inflatable seat belt apparatus"), force applied to the occupant can be distributed over the range wider than the conventional webbing so as to decrease the stress applied to the occupant and a higher safety efficiency can be provided.
The inflatable seat belt apparatus is effective even for a rear seat. For mounting an air bag apparatus for an occupant on the rear seat, the air bag apparatus is generally mounted on the rear side of the back portion of the front seat. It is necessary that the front seat structure has a high rigidity for suitably operating the air bag apparatus for the rear seat to efficiently restrain and secure the occupant. However, it is difficult to provide the reclining mechanism having a movable portion to the front seat if the air bag apparatus is mounted on the rear side of the back portion of the front seat. Therefore, the inflatable seat belt apparatus is effective for the rear seat because the inflatable seat belt apparatus can be independently mounted on the rear seat and has no restriction such as the above mentioned air bag apparatus.
In such an inflatable seat belt apparatus, wherein the envelope shaped portion is folded to form a band shaped belt having a predetermined width as mentioned above, the folded envelope shaped portion is piled up to be thickened. Therefore, the belt is hard to fit the occupant's body during wearing and hard to pass smoothly a slip guide of a pillar anchor. Accordingly, there is a fear of decreasing the belt wearing rate because the occupant feels an incongruity during wearing.
Further, the folded portions are glued together and therefore, the inflatable portion is hard to deploy smoothly even when the spouted gas is introduced into the envelope shaped portion during the deployment.
Therefore, the applicant has already proposed an inflatable seat belt apparatus which can overcome these problems (Japanese Patent Application No. 210353/1992, 210355/1992).
These applications disclose inventions that the envelope shaped portion is structured by a knitted fabric member, i.e. a woven textile member having wefts which expands enough.
According to these inventions, the seat belt apparatus is maintained in a relatively thin band shape and can inflate and develop the envelope shaped portion reliably and promptly at an emergency.
FIG. 1 (a) shows an example of the inflatable seat belt apparatus, wherein one portion of a shoulder belt is structured by a cylindrical knitted fabric member.
And a rubber tube formed in an envelope shape is inserted into the cylindrical knitted fabric member.
In this figure, numeral 51 designates a tongue. The tongue 51 has a gas inlet 53 for introducing gas into the rubber tube in a belt 52 inside thereof. The gas inlet 53 is coupled to a gas outlet of gas generating means, i.e. gas generator (not shown), connected inside a buckle 54 when the tongue 51 is engaged with the buckle 54 for fixing a belt end 52a to the vehicle body.
FIG. 1 (b) shows an example of a state where a predetermined gas pressure is applied to the belt portion of the inflatable seat belt apparatus structured as stated above.
As shown in this figure, the rubber tube is inflated by the gas pressure in the tube. And a whole shape of the rubber tube is defined by the envelope shaped knitted fabric member wrapping the tube and is inflated in a spindle shape. Because the area of the belt portion touching the chest and the like of the occupant is increased, an impact applied to the occupant is softened and the apparatus can protect the occupant efficiently.
Because the inflatable portion formed in an envelope shape is radially increased, the length of the belt in a longitudinal direction is shortened by .DELTA.L. Therefore, the inflatable seat belt apparatus has a function as a pre-tensioner so that the occupant is more effectively retained.
However, the following problems become apparent from various tests using a model and a real vehicle for the inflatable seat belt apparatus as mentioned above. The tests are executed by using a full-sized dummy.
As shown in FIG. 2, the knitted fabric structural portion of the shoulder belt 52 is effectively inflated and deployed in a crash.
When the belt tries to restrain the dummy D from movement, the gas in the tube escapes to a space 52b between the buckle near the floor and the waist of the dummy D and to a space 52c between a pillar anchor 55 and the shoulder of the dummy D, so that the shoulder belt 52 is inflated in a gourd shape. In this state, the shoulder belt 52 can not be inflated over an enough area at the important place for catching the chest of the dummy D. This spoils the merit of using an inflatable structure for the shoulder belt.
Because the tube is inflated in the whole extent of the longitudinal direction thereof, the inflation volume becomes large and then the gas pressure in the tube is hard to be increased. In addition, because the tube can not be inflated enough in the radial direction thereof, the length of the belt in the longitudinal direction is not shorted enough. Therefore, the above mentioned function as a pre-tensioner does not work effectively.
Furthermore, the above mentioned inflatable seat belt apparatus has various inconveniences. In the inflatable seat belt apparatus, the envelope shaped portion of the shoulder belt is also wound in an ELR mounted in the under portion in the pillar. The belt portion formed of the knitted fabric is slightly thicker than the belt portion formed of the fabric textile. Therefore, the ELR should be exchanged for a special ELR which can accommodate the thick belt formed of a knitted fabric.
A slip guide is mounted to the pillar anchor to change the direction of the belt withdrawn form ELR. The slip guide has a guide opening for the belt. The width of the guide opening is narrow for preventing the belt from twisting and turning over. Therefore, it is hard to allow the thick belt to smoothly pass therethrough.
On the other hand, in case that the belt is formed to have a short width, the occupant feels the belt is undependable. The belt must maintain its stiffness and its form which give dependence to the occupant when the occupant uses the belt.
It should be considered to prevent the surface of the knitted fabric from abrasion.